On Tue, Sep 22, 2020 at 10:08 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > On Tue, Sep 22, 2020 at 03:56:47PM +0200, Miklos Szeredi wrote: > > On Wed, Sep 16, 2020 at 6:18 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > > > > But if this is non-truncate setattr then server will not kill suid/sgid. > > > So continue to send ATTR_MODE to kill suid/sgid for non-truncate setattr, > > > even if ->handle_killpriv_v2 is enabled. > > > > Sending ATTR_MODE doesn't make sense, since that is racy. The > > refresh-recalculate makes the race window narrower, but it doesn't > > eliminate it. > > Hi Miklos, > > Agreed that it does not eliminate that race. > > > > > I think I suggested sending write synchronously if suid/sgid/caps are > > set. Do you see a problem with this? > > Sorry, I might have missed it. So you are saying that for the case of > ->writeback_cache, force a synchronous WRITE if suid/sgid is set. But > this will only work if client sees the suid/sgid bits. If client B > set the suid/sgid which client A does not see then all the WRITEs > will be cached in client A and not clear suid/sgid bits. Unless the attributes are invalidated (either by timeout or explicitly) there's no way that in that situation the suid/sgid bits can be cleared. That's true of your patch as well. > > Also another problem is that if client sees suid/sgid and we make > WRITE synchronous, client's suid/sgid attrs are still cached till > next refresh (both for ->writeback_cache and non writeback_cache > case). So server is clearing suid/sgid bits but client still > keeps them cached. I hope none of the code paths end up using > this stale value and refresh attrs before using suid/sgid. > > Shall we refresh attrs after WRITE if suid/sgid is set and client > expects it to clear after WRITE finishes to solve this problem. Or > this is something which is actually not a real problem and I am > overdesigning. The fuse_perform_write() path already has the attribute invalidation, which will trigger GETATTR from fuse_update_attributes() in the next write. So I think all that should work fine. Thanks, Miklos
